It is known that the hull friction resistances in water will become smaller by supplying air bubbles to the surface of a moving hull.
A pipe is attached along lateral aspects of the hull as a means to send air to the bubble generator prepared in the ship's bottom (lateral surface), and a means to supply air with this pipe is described in JP 11-180380 A (Prior art 1) and JP 2000-296796 A (Prior art 2).
In order to reduce frictional resistances effectively, it is desirable that bubbles stop at the hulls surfaces for a long time, and, for that purpose, it is required that bubble diameter should be small as possible. Such microbubbles are generated according to the Kelvin-Helmholtz Instability Phenomenon as described in JP 2002-2582 A (Prior art 3).
Prior art 3 describes that, preparing a recess in the shell (immersion surface) of a ship's bottom, and connecting a gas tube which supplies air to this recess, negative pressure portion having a wedge shape is attached to the upper stream side of a recess, and generates the Kelvin-Helmholtz-instability phenomenon to make microbubbles in a recess.
Moreover, in JP 4070385 A (Prior art 4), the technology of employing a wing is disclosed as a means which make microbubbles instead of the wedge-shaped negative pressure formation part disclosed to the patented documents 3.
[Prior Art 1] JP11-180380 A
[Prior Art 2] JP2000-296796 A
[Prior Art 3] JP2002-2582 A
[Prior Art 4] JP4070385